If your arthritis does not respond to the non-surgical treatments, there are different kind of surgical options for prosthetic knee replacement. The individual components for the femor and tibia are made of metal while the insert between femoral and tibial components is made from a special polyethylene. In case of metal allergy, there are also ceramic implants combined with all polyethylene components.
UNICOMPARTMENTAL KNEE PROSTHESIS : There are some pathologies where only one part of the knee, either the inside or medial or the outside or lateral "compartment", needs to be replaced. If only one side of the joint is damaged, smaller implants can be used, known as unicompartmental knee replacement, to resurface just the affected side on the femur and tibia.
TOTAL KNEE PROSTHESIS : Although the overall designs of total knee implants vary, typical total knee replacement implants have three basic parts, the femoral, the tibial and the patellar component.
• The femoral component is generally made of metal and curves around the end of the femur (your thighbone). There is a groove down the center of the front part of the femoral implant which allows the patella, or kneecap, to move up and down as the knee bends and straightens.
• The tibial component is a flat metal platform with a polyethylene (plastic) insert or spacer. This component varies in structure, depending on the type of surgery performed.
• The patellar implant is a dome-shaped piece of polyethylene that re-surfaces the back of the kneecap.
CRUCIATE-RETAINING DESIGNS :As the name implies, the natural posterior cruciate ligament is kept with this implant design. Cruciate-retaining implants do not have what is known as a center post and cam design. This implant may be appropriate for a patient whose posterior cruciate ligament is healthy enough to continue stabilizing the knee joint.
POSTERIOR-STABILIZED DESIGNS : Posterior-stabilized designs are used whrn the natural posterior ligament is damaged or torn and cannot be retained to help stabilze the joint. In these designs, the polyethylene insert of the tibial component has a raised surface with an internal post that fits into a special bar (called a cam) in the femoral component. The pieces work together to do what the natural posterior cruciate ligament does, prevent the thighbone from sliding forward too far on the shinbone when you bend your knee.
REVISION COMPONENTS : All of the above described prostheses can fail because for many different reasons and have to be replaced by Revision Components.
The longevity and performance of any knee replacement depends on several factors, including your activity level, weight, and general health. Just as wear in the natural joint contributed to the need for a replacement, wear in the implant may eventually require a second surgery (called a revision).
Revision surgery may require special components. Typically they will have longer stems which fit into the femur and tibia and they may have attached metal pieces called augments which substitute for bone defects or missing pieces of bone.
Revision components often have a cam in the center of the knee similar to a posterior stabilized component. In revision components, though, the cam is larger to give the knee more stability.
In cases where the knee is very unstable and a large amount of bone is missing, it may be necessary to join the femur and tibia together with a linked "hinge" in the center of the joint.